This invention relates to an image forming apparatus employing an electrophotographic method used in a copying machine, a printer, etc.
In recent years, for a copying machine, a printer, etc. for which a high speed and a high image quality are required, image forming method of an electrophotographic type has been mostly used.
The reason is, for example, that a high-speed and high-quality image can be obtained stably by an electrophotographic method, and on top of it, it can cope with the requirement for formation of a digital image or a color image. Hence, it can be considered that this tendency will continue also from now on; therefore, as regards an image forming method of an electrophotographic type, it is true that further improvement of performance is required in several points, and the most important point among them is image quality.
The most effective way for the improvement of image quality is to make the particle diameter of the toner small, or to make the particles have a suitable shape uniformly, accompanied by incorporating, in the inside of an apparatus, a mechanism to keep proper the condition of image forming in the apparatus. However, owing to these ways for improvement influencing other characteristics to deteriorate them, some characteristics which have heretofore been of no problem are now regarded as a problem.
To state the above-mentioned problem concretely, in order to improve image quality, it is advantageous to use a toner having a small particle diameter, or to use a toner whose shape has no remarkable concave or convex portions and is nearly spherical as much as possible. However, any one of these necessary conditions for a toner acts disadvantageously on the cleaning of a photoreceptor. That is, if other conditions are kept the same, the smaller the diameter of a toner becomes, or the less concave and convex portions the particles of a toner have on their surface, the larger their contact surface becomes relatively to the volume of the particles when they adhere to the surface of a photoreceptor; therefore, cleaning becomes more difficult.
On top of it, for the purpose of detecting whether or not the toner is supplied with an amount enough to produce the maximum density as a process for keeping image quality at a high level, it is necessary to form a patch image for the detection directly outside the image transfer area of a photoreceptor. Further, in order to perform cleaning uniformly, for example, the surface of a photoreceptor must be smoothly rubbed by a cleaning blade, and for checking it, it is put into practice that band-shaped toner images extending over the whole width of the photoreceptor are formed at specified intervals and removed for cleaning.
In particular, in an apparatus having a high image forming speed, owing to the large frictional force acting between the photoreceptor surface and the cleaning member, a smoothing agent composed of zinc stearate particles or the like is properly used to make the surface easy to be cleaned by scraping, to prevent a failure such as reverse bending of the cleaning blade tip.
The toner images to be formed for the above-mentioned reason are such that are not transferred onto a transfer material originally and do not appear on a final image (non-transferred visible image), and they are all formed with a toner amount enough to exhibit the maximum density; therefore, they have a large toner deposition quantity per unit area, to tend to cause poor cleaning. In the case where this process is carried out in combination with a toner having a small particle diameter or a toner having a proper particle shape uniformly, as a matter of course, the tendency to cause poor cleaning becomes strengthened. If it happens, in the case where the poorly cleaned part comes within the image area at the time of next image forming, the image is to appear on the final image. In another way, in the case where the image is the patch image for detecting image density and overlaps the next one, if the toner image of the previous time remains, the image is to be detected as one having a higher density than original one.
It is an object of this invention to provide an image forming apparatus employing an electrophotographic method capable of causing no poor cleaning and keeping a high image quality over a long period of time, while using a toner having a small particle diameter, a uniform shape, or a shape without protrusions, as a result of the improvement in the above-mentioned points of problem.
The object of this invention can be accomplished by any one of the structures (1) to (22) described below.
(1) An image forming apparatus using a toner having a volume average particle size of 2 to 8 xcexcm, comprising a charging device for uniformly charging a photoreceptor, a developing device for developing an image obtained by image exposure by said toner, a transfer device for transferring a toner image to a transfer material, a fixing device for fixing, and a cleaning device for cleaning the photoreceptor after the transfer of a toner image, and carrying out image formation by using repeatedly the photoreceptor after cleaning, wherein it is employed a mechanism such that, in the case where a toner image which is not to be transferred is formed on the photoreceptor, an image formation is performed after cleaning is done a plurality of times for an area on which the above-mentioned toner image has been formed in the previous process.
(2) An image forming apparatus as set forth in the structure (1), wherein the volume average particle size of the toner is 3 to 7 xcexcm.
(3) An image forming apparatus using a toner having a volume average particle size of 2 to 8 xcexcm, comprising a charging device for uniformly charging a photoreceptor, a developing device for developing an image obtained by image exposure by said toner, a transfer device for transferring a toner image to a transfer material, a fixing device for fixing, and a cleaning device for cleaning the photoreceptor after the transfer of a toner image, and carrying out image formation by using repeatedly the photoreceptor after cleaning, wherein it is employed a mechanism such that, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed in such a way that the image does not overlap the area on which the above-mentioned toner image has been formed in the previous process.
(4) An image forming apparatus as set forth in the structure (3), wherein the volume average particle size of the toner is 3 to 7 xcexcm.
(5) An image forming apparatus using a toner containing toner particles having a coefficient of shape falling within a range of 1.0 to 1.6 of an amount of at least 65% by number, comprising a charging device for uniformly charging a photoreceptor, a developing device for developing an image obtained by image exposure by said toner, a transfer device for transferring a toner image to a transfer material, a fixing device for fixing, and a cleaning device for cleaning the photoreceptor after the transfer of a toner image, and carrying out image formation by using repeatedly the photoreceptor after cleaning, wherein it is employed a mechanism such that, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed after cleaning is done a plurality of times for an area on which the above-mentioned toner image has been formed in the previous process.
The coefficient of shape mentioned above represents the ratio of an area of a circle with a diameter which is a projected maximum size of a toner particle to a projected area of the toner particle.
(6) An image forming apparatus as set forth in the structure (5), wherein a toner containing toner particles having the coefficient of shape falling within a range of 1.2 to 1.6 of an amount of at least 65% by number is used.
(7) An image forming apparatus using a toner containing toner particles having a coefficient of shape falling within a range of 1.0 to 1.6 of an amount of at least 65% by number, comprising a charging device for uniformly charging a photoreceptor, a developing device for developing an image obtained by image exposure by said toner, a transfer device for transferring a toner image to a transfer material, a fixing device for fixing, and a cleaning device for cleaning the photoreceptor after the transfer of a toner image, and using the photoreceptor after cleaning repeatedly to form an image, wherein it is employed a mechanism such that, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed in such a way that the image does not overlap the area on which the above-mentioned toner image has been formed in the previous process.
(8) An image forming apparatus as set forth in the structure (7), wherein a toner containing toner particles having the coefficient of particle shape of 1.2 to 1.6 at least 65% by number is used.
(9) An image forming apparatus using a toner containing toner particles having no protrusion of an amount of at least 50% by number, comprising a charging device for uniformly charging a photoreceptor, a developing device for developing an image obtained by image exposure by said toner, a transfer device for transferring a toner image to a transfer material, a fixing device for fixing, and a cleaning device for cleaning the photoreceptor after the transfer of a toner image, and using the photoreceptor after cleaning repeatedly to form an image, wherein it is employed a mechanism such that, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed after cleaning is done a plurality of times for an area on which the above-mentioned toner image has been formed in the previous process.
(10) An image forming apparatus using a toner containing toner particles having no protrusion of an amount of at least 50% by number, comprising a charging device for uniformly charging a photoreceptor, a developing device for developing an image obtained by image exposure by said toner, a transfer device for transferring a toner image to a transfer material, a fixing device for fixing, and a cleaning device for cleaning the photoreceptor after the transfer of a toner image, and using the photoreceptor after cleaning repeatedly to form an image, wherein it is employed a mechanism such that, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed in such a way that the image does not overlap the area on which the above-mentioned toner image has been formed in the previous process.
(11) An image forming apparatus as set forth in any one of the structures (1) to (10), wherein the aforesaid toner image which is not to be transferred is a patch image for detecting image density, or a band-shaped image extending in the width direction of the photoreceptor formed on at least one of the leading edge portion and the trailing edge portion of the image area.
(12) An image forming method using a toner having a volume average particle size of 2 to 8 xcexcm, and repeating a process comprising the steps of uniformly charging a photoreceptor, developing an image obtained by image exposure by said toner, transferring and fixing the obtained toner image onto a transfer material, and cleaning the photoreceptor after the toner image is transferred for reuse, wherein, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed after cleaning is done a plurality of times for an area of the photoreceptor on which the above-mentioned toner image has been previously formed.
(13) An image forming method as set forth in the structure (12), wherein the volume average particle size of the toner is 3 to 7 xcexcm.
(14) An image forming method using a toner having a volume average particle size of 2 to 8 xcexcm, and repeating a process comprising the steps of uniformly charging a photoreceptor, developing an image obtained by image exposure by said toner, transferring and fixing the obtained toner image onto a transfer material, and cleaning the photoreceptor after the toner image is transferred for reuse, wherein, in the case where a toner image which is not to be transferred is formed on the photoreceptor, an image formation is performed in such a way that the image does not overlap the area on the photoreceptor on which the above-mentioned toner image has been previously formed in the previous process.
(15) An image forming method as set forth in the structure (14), wherein the volume average particle size of the toner is 3 to 7 xcexcm.
(16) An image forming method using a toner containing toner particles having a coefficient of particle shape falling within a range of 1.0 to 1.6 of an amount of at least 65% by number, and repeating a process comprising the steps of uniformly charging a photoreceptor, developing an image obtained by image exposure by said toner, transferring and fixing the obtained toner image onto a transfer material, and cleaning the photoreceptor after the toner image is transferred for reuse, wherein, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed after cleaning is done a plurality of times for an area of the photoreceptor on which the above-mentioned toner image has been previously formed.
(17) An image forming method as set forth in the structure (16), wherein a toner containing toner particles having the coefficient of shape falling within a range of 1.2 to 1.6 of an amount of at least 65% by number is used.
(18) An image forming method using a toner containing toner particles having a coefficient of shape falling within a range of 1.0 to 1.6 of an amount of at least 65% by number, and repeating a process comprising the steps of uniformly charging a photoreceptor, developing an image obtained by image exposure by said toner, transferring and fixing the obtained toner image onto a transfer material, and cleaning the photoreceptor after the toner image is transferred for reuse, wherein, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed in such a way that the image does not overlap the area on the photoreceptor on which the above-mentioned toner image has been previously formed in the previous process.
(19) An image forming method as set forth in the structure (18), wherein a toner containing toner particles having the coefficient of shape falling within a range of 1.2 to 1.6 of an amount of at least 65% by number is used.
(20) An image forming method using a toner containing toner particles having no protrusion of an amount of at least 50% by number, and repeating a process comprising the steps of uniformly charging a photoreceptor, developing an image obtained by image exposure by said toner, transferring and fixing the obtained toner image onto a transfer material, and cleaning the photoreceptor after the toner image is transferred for reuse, wherein, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed after cleaning is done a plurality of times for an area of the photoreceptor on which the above-mentioned toner image has been previously formed.
(21) An image forming method using a toner containing toner particles having no protrusion of an amount of at least 50% by number, and repeating a process comprising the steps of uniformly charging a photoreceptor, developing an image obtained by image exposure by said toner, transferring and fixing the obtained toner image onto a transfer material, and cleaning the photoreceptor after the toner image is transferred for reuse, wherein, in the case where a toner image which is not to be transferred is formed on the photoreceptor, image formation is performed in such a way that the image does not overlap the area on the photoreceptor on which the above-mentioned toner image has been previously formed in the previous process.
(22) An image forming method as set forth in any one of the structures (12) to (21), wherein the aforesaid toner image which is not to be transferred is a patch image for detecting image density, or a band-shaped image extending in the width direction of the photoreceptor formed on at least one of the leading edge portion and the trailing edge portion of the image area.
This invention is such one as to provide an image forming apparatus, while using a toner having a small particle diameter or a toner whose surface shape has no remarkable concave or convex portions, and incorporating a countermeasure against poor cleaning owing to patch image formation for detecting image density or formation of band-shaped images extending over the whole width of the photoreceptor at specified intervals, capable of preventing problems which are newly produced therein beforehand, and accomplishing a high-speed and high-quality image formation stably over a long period of time.
Besides, in the explanation of this invention, its aspects are sometimes called in the following way.
First aspect: the aspect having the structure set forth in any one of the structures (1) to (4), and (12) to (15);
Second aspect: the aspect having the structure set forth in any one of the structures (5) to (8), and (16) to (19); and
Third aspect: the aspect having the structure set forth in any one of the structures (9) and (10), and (20) and (21).